Method for transporting gas



Jan. 30, 1968 A. L. VAN KLEEF 3,365,393

METHOD FOR TRANSPORTING GAS Filed May 9, 1966 2 Sheets-Sheet 1 FIG. 2

INVENTOR: V

ALFRED L.VAN KLEEF FIG. 3 BY: ,7. OJ%

HIS AGENT Jan. 30, 1968 L, VAN E F 3,365,898

METHOD FOR TRANSPORTING GAS Filed May 9, 1966 2 Sheets-Sheet 2 INVENTOR;

ALFRED L.VAN KLEEF HIS AGENT United States Patent 3,365,898 METHOD FOR TRANSPORTING GAS Alfred L. Van Kleef, The Hague, Netherlands, assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed May 9, 1966, Ser. No. 548,542 Claims priority, application Netherlands, June 3, 1965, 657,i)60 Claims. (CI. 62-55) ABSTRACT OF THE DISCLOSURE A method is provided for transporting natural gas or methane by ship or other vehicle in the liquid state. The gas is liquefied on the ship during loading by passing it in heat exchange with a cold liquid present on the ship. The liquefied gas and the warmed-up liquid heat exchange fluid are stored in tanks on the ship which then transports it to a desired destination. In the destination port the liquefied gas is re-gasified on the ship by passing it in heat exchange with the warmed-up liquid present on the ship. The liqud thus cooled down is stored again in the cold condition in tanks on the ship to be used for liquefying the next load of gas.

The invention relates to a method for transporting a gas, in particular natural gas or methane, by means of a vehicle from a reception point to a delivery point.

It is known to transport gas in liquid form from a reception point to a delivery point, for example by ship from an exporting port to an importing port. A drawback of the known methods is that both in or near the exporting port and in or near the importing port complicated and expensive installations are necessary to liquefy the gas and to gasify the liquefied gas again. This means that these known methods are not very flexible. It would be attractive if the gas could be supplied to the ship in the exporting port in the gaseous state and could be discharged as gas by the ship in the importing port. Such a method would possess great flexibility, since gas could be transported by ship between all ports where gas is available for export, and all ports where it is desired to import gas, without it being necessary to construct the said complicated installations in or near these ports for liquefying and re-gasifying the gas. Moreover, a method of this type would have the advantage that relatively simple harbor facilities would be sufiicient for the supply and discharge of gas to and from the ship. Thus the loading and unloading might be carried out, for example, with offshore loading and unloading buoys, to which the ship A is moored. A buoy of this type is described, for example, in U.S. Patent No. 3,187,355. This object could be achieved by transporting the gas in gaseous form. This is not very attractive, however, since only a small quantity of gas can be tranported per volume unit of tank space compared with the transport of gas in liquid form.

The object of the invention is to provide a method of the above type from which the above drawbacks are absent.

This invention relates to a method for transporting a gas, particularly natural gas or methane, by means of a vehicle from a reception point to a delivery point which comprises the steps of:

(a) Supplying a gas to the vehicle at the reception point;

(b) Liquefying the gas on or in the vehicle by removing heat therefrom;

(c) Passing the liquefied gas into tanks situated on or in the vehicle;

(d) Transferring the vehicle from the reception point to the delivery point;

3,365,898 Patented Jan. 30, 1968 ice (e) converting the liquefied gas, on or in the vehicle, into the gaseous state by supplying heat thereto at the delivery point; and

(f) Discharging the gas from the vehicle at the delivery point.

In order to ensure that the installation, on or in the vehicle, which is necessary to liquefy or gasify the gas, is as small and simple as possible, and in order to keep the consumption of energy to a minimum, the removal of heat according to step (b) is effected according to the invention at least partly by bringing the gas into heat exchange with a fluid. Similarly, the supply of heat according to step (e) is eifected at least partly by bringing the liquefied gas into heat exchange with a fluid.

This fluid is preferably supplied from tanks situated on or in the vehicle, whereupon the said heat exchange takes place, after which the fluid is passed back again into tanks situated on or in the vehicle.

The fluid employed is preferably of a type which invariably remains in the liquid state, for example isopentane.

The method according to the invention will now be described with reference to the drawing in which:

FIGURE 1 shows diagrammatically a procedure for liquefying the gas;

FIGURE 2 shows diagrammatically a procedure for gasifying the liquefied gas;

FIGURE 3 shows diagrammatically a procedure for starting up the method according to the invention;

FIGURE 4 shows diagrammatically an alternative procedure for liquefying the gas;

FIGURE 5 shows diagrammatically an alternative procedure for gasifying the liquefied gas; and

FIGURE 6 shows diagrammatically an alternative procedure for starting up the method.

Let it be assumed that the transport vehicle is a ship lying in a port the reception point, from where the gas, for example natural gas, must be dispatched. The natural gas is passed to the ship at a pressure of 40 atm. abs. via a line 1 shown in see FIGURE 1. The gas is then passed on via lines 2 and 3 to a compressor 5 and a compressor 4 respectively. In the compressors 4 and 5 the natural gas is compressed, for example to a pressure of atm. abs. The compressed natural gas is then cooled in the conventional manner by means of heat-exchangers 6 and 7, which are, for example, water-cooled. The compressed natural gas flows from heat exchanger 6 via line 8 to line 10, and the compressed gas from heat exchanger 7 flows via line 9 to line 10. Line 10 conveys the compressed natural gas to heat exchanger 11. The compressed natural gas isliquefied in the heat exchanger 11 by means of a very cold fluid, for example isopentane at a temperature of 160 C., which is passed via line 17, heat exchanger 15 and line 18 to the heat exchanger 11. In the heat exchanger 11 the isopentane gives off cold and thus rises in temperature, whereupon it leaves the heat exchanger 11 via line 19. The natural gas, cooled and liquefied in heat exchanger 11, flows via line 12, in which an expansion valve 13 is arranged, to an expansion vessel 14 which is provided with a liquid/ gas separator 40. In the expansion valve 13 the liquefied natural gas is expanded to the desired storage pressure, for example of 1 atm. abs. The liquefied natural gas then passes through the heat exchanger 15 in which, further cooling takes place. and flows on through line 16 to preferably heat-insulated ships tanks wherein the liquefied natural gas is stored. The cold isopentane which is passed through the heat exchangers 15 and 11, as mentioned above, is supplied via the line 17, preferably from ships tanks which are heatinsulated. After the isopentane has passed through the heat exchangers 15 and 11 with the result that its tem- 3 perature rises it is passed through the line 19 to tanks which are preferably situated on the ship. Once the ship has loaded its cargo of natural gas it leaves the reception point and sails to a port where the gas has to be delivered, called the delivery point. In the latter port the unloading can be effected as shown in FIGURE 2. The liquefied natural gas present in the ships tanks is passed through a line 20 to the expansion vessel 14, for example by means of a suitable pump. The liquefied natural gas thereupon flows via the heat exchanger 15, where it absorbs a certain amount of heat, to line 21 in which a pump 22 is arranged. The pump 22 compresses the liquefied natural gas to a pressure of, for instance, 40 atm. abs. The liquefied natural gas flows via the pump 22 through the heat exchanger 11 in which it absorbs heat and passes over into the gaseous state. Finally, the gaseous natural gas flows through line 23, at a pressure of, for example, 40 atm. abs., to the shore where the natural gas is taken up into a gas network or a storage tank. As mentioned above, the liquefied natural gas absorbs heat in the heat exchangers 15 and 11. For this purpose heat is passed to these heat exchangers, for example by means of isopentane. Preferably this isopentane is present in ships tanks and will be the same isopentane which was used during loading of the ship to cool a quantity of natural gas, as a result of which the isopentane rose in temperature, as mentioned earlier. The isopentane is passed via the line 19 through the heat exchanger 11, from there via the line 18 to the heat exchanger 15 and finally via the line 17 preferably to heat-insulated ships tanks. While passing through the heat-exchangers 11 and 15 the isopentane is cooled down considerably, for example to approximately 160 C. Since the temperature of the isopentane is very low it is desirable to store it in heat-insulated ships tanks so that the cold is not lost during the voyage from the delivery port to the reception port. In due course, the cooled isopentane can then be used again at the reception port for liquefying a subsequent cargo of natural gas on board the ship.

While passing through the heat exchanger 15 the liquefied natural gas absorbs a certain amount of heat, as a result of which a relatively small part of the liquefied natural gas passes over into the gaseous state. This gaseous natural gas, which has a storage pressure of, for example, 1 atm. abs. and a storage temperature of, for example, -160 C. is passed via a line 25 through a heat exchanger 26 in which the temperature of the natural gas rises. From the heat exchanger 26 the natural gas flows via compressor 27, line 28, after-cooler 29 which may be Water-cooled, line 28, compressor 4, after-cooler 6 and line 8 to line 23 in which the natural gas mixes with the natural gas which is being carried to the shore via the line 23. In the compressors 27 and 4 the natural gas is brought up to the same, or approximately the same, pressure as that of the natural gas in the line 23. The heating of the natural gas flowing through the heat exchanger 26 is effected by heat exchange with isopentane which is cooled as a result and which is preferably stored in the cold state in heat-insulated ships tanks after this cooling. The isopentane is supplied via line 30, preferably from ships tanks, whereupon it passes through the heat exchanger 26 in which it is cooled, and is subsequently carried off via line 31 preferably into heatinsulated ships tanks. In due course this cold isoptenane can be used again in the reception port for liquefying a new cargo of natural gas.

The procedure for starting up the method described will now be explained with reference to FIGURE 3.

It will be obvious that in order to be able to liquefy a cargo of natural gas at the reception point, for example the port from which the gas has to be shipped, it is necessary to have sufficient cold available for this purpose, for example in the form of a quantity of cold isopentane. For this purpose isopentane, for example at ambient temperature, is passed from ships tanks via line 30 to the heat exchanger 26. In the heat exchanger 26 this isopentane is cooled, for example to -l60 C., whereupon it is passed via the line 31 to preferably heatinsulated ships tanks. In this manner a quantity of isopentane is cooled, which quantity is at least sufficiently large to liquefy a cargo of natural gas in the reception port, but which is also large enough to compensate for cold losses occurring as a result of heat transfer during transportation. The heat exchanger 26 is cooled by means of natural gas, that is to say by the expansion of natural gas having a high pressure, for example 160 atm. abs., which is fed via line 36 to at least one expansion turbine 37. After expansion has been carried out in the turbine 37, for example to 1 atm. abs., a mixture of gas and liquid is formed, having a temperature of, for example, -l60 C., which is passed via line 38 to the expansion vessel 14. Cold natural gas, for example having a temperature of 160 C., is drawn in through th compressor 27 via the line 25. The cold natural gas consequently passes through the heat exchanger 26, in which it gives off part of its cold so that the isopentane in the heat exchanger 26 is cooled down. In the compressor 27 the natural gas is compressed, for example to 10 atm. abs., whereupon it fiows to compressor 4 via line 28 and after-cooler 29. The compressor 4 compresses the gas, for example, to a pressure of 40 atm. abs. whereupon the gas flows t0 compressor 5 via line in which an after-cooler 6 is arranged. The compressor 5 further compresses the gas, for example, to 160 atm. abs. whereupon the gas, having passed through after-cooler 7, flows via line 36 to the expansion turbine 37, where the procedure described above is repeated.

An alternative system for liquefying and gasifying the natural gas and for starting up the method will now be described with reference to FIGURES 4, 5 and 6.

The liquefaction of natural gas as shown in FIGURE 4 proceeds as follows.

In the exporting port, the reception point, the natural gas is passed via a line 50 to the ship on which the installation for liquefying the gas is situated. The natural gas is supplied, for example, at a pressure of atm. abs. and flows via the line to compressor 51, in which the natural gas is compressed to a pressure of for example 160 atm. abs. The natural gas flows via line 52 in which is arranged an after-cooler 53 which is, for example, watercooled to a heat-exchanger 54 and from there via line 55 to a second heat exchanger 56. In the heat exchangers 54 and 56 the natural gas is liquefied, whereupon it flows via line 57, expansion valve 58 and line 59 under expansion, for example to 1 atm. abs., into expansion vessel 60. Any gas formed is carried off via line 61 and the liquefied natural gas is carried off via line 62 to preferably heat-insulated ships storage tanks. The heat exchangers 54 and 56 are cooled by passing cold isopentane having a temper ture of, for example, 160 C. through them. This cold isopentane is supplied via line 63, flows via the heat exchanger 56 and from there via line 64 to the heat exchanger 54. After having undergone a rise in temperature to, for example, 27 C. the isopentane leaves the heat exchanger 54 via line 65. The isopentane flows via the line 65 to tanks situated on the ship where it is stored. Once the ship has been loaded with liquid natural gas it sails to the importing port, the delivery point. At this point the liquefied natural gas must be gasified again on the ship, so that the ship can deliver the natural gas in gaseous form. This takes place as shown in FIGURE 5.

The liquefied natural gas is passed from ships tanks to the expansion vessel 60, via a line 66. The liquefied natural gas leaves the expansion vessel 64] via a line 68, whereupon it is compressed by means of a pump 67 to a desired pressure, for instance 40 atm. abs. or more, whereupon it is passed to the heat exchanger 56. The liquefied natural gas absorbs heat in heat exchanger 56 whereupon it fiows via the line 55 to the heat exchanger 54 in which it likewise absorbs heat and passes over into the gaseous state.

The gaseous natural gas finally leaves the ship through a line 70 and on shore is fed into a gas distribution network or is put into storage. Heat is supplied to the heat exchangers 54 and 56 by passing relatively warm isopentane, for example at a temperature of 27 C., from ships tanks via the line 65 to the heat exchanger 54, and from there via the line 64 to the heat exchanger 56-. The isopentane gives off its heat in the heat exchangers 54 and 56, being thereby cooled, for example to -160= C. This cold isopentane is finally passed from the heat exchanger 56 via the line 63 to preferably heat-insulated ships tanks in which the cold isopentane is stored so that in due course it can be used again for liquefying a new cargo of natural gas being loaded in the exporting port.

The procedure for starting up the method described above Will now be described with reference to FIGURE 6.

The heat-exchanger 54 has an extra pipe bundle 75 which is not used in the methods according to FIGURES 4 and 5. In the present method, however, the bundle 75 is indeed used, as will be seen from the following.

Nitrogen gas having a pressure of, for example, 17 atm. abs. and a temperature of, for example, 17 C. is drawn up by compressor 51 via a line 76. This gas is compressed in compressor 51 to a pressure of, for example, 160 atm. abs. whereupon it is passed via the line 52 to the aftercooler 53. In the after-cooler 53 the nitrogen gas is cooled to a temperature of, for example, 27 C. This gas now splits into two streams. One stream flows via a line 77 to the bundle 75 of the heat exchanger 54 in which the nitrogen gas is cooled, for example, to -79 C. From the bundle 75 this cold nitrogen gas flows via line 78 to an expansion turbine 79 in which the nitrogen gas expands, for example to a pressure of 17 atm. abs. This expansion is accompanied by a drop in temperature, for example to -160 C., and formation of a small quantity of liquid nitrogen e.g., 5%. This cold mixture is passed via line 89 to the heat-exchanger 56, where it absorbs heat. The cold nitrogen then flows from the heat exchanger 56 via the line 55 to the heat exchanger 54 where the nitrogen again absorbs heat and rises in temperature. The nitrogen, which now has a temperature of, for example, 17 C. and a pressure of 17 atm. abs. flows from the heat-exchanger 54 to the compressor 51. Another part of the nitrogen gas flows from the after-cooler 53 via a line 81 to an expansion turbine 82. There the nitrogen gas expands, for example to a pressure of 17 atm. abs, accompanied by a drop in temperature to, for example, 95 C. This cold nitrogen gas flows via line 83 to the line 55, whereupon it flows back via the heat-exchanger 54 and the line 76 to the compressor 51. The cold nitrogen gas absorbs heat in the heatr exchanger 54, with the result that its temperature rises. It follows from the preceding remarks that cold is available in the heat exchangers 54 and 56 which can be used for cooling a quantity of isopentane. For this purpose isopentane having a temperature of, for example 27 C. is passed via the line 65 to the heat exchanger 54. The temperature of the isopentane is lowered in heat exchanger 54, whereupon the isopentane is passed via the line 64 to the heat exchanger 56 where it is further cooled so that the isopentane finally reaches a temperature of, for example, -160 C. This cold isopentane is then passed via the line 63 to preferably heat-insulated ships tanks where it is stored until the ship arrives in the natural gas exporting port where it is used for liquelying a cargo of natural gas loaded on to the ship in the gaseous state. In addition to being used for starting up the method, the system according to FIGURE 6 can also be used to compensate cold losses as a consequence of heat transfer occurring during the transportation of the liquefied natural gas.

The systems according to FIGURES 1, 2 and 3 are combined to form a single installation, situated on a ship. The systems according to FIGURES 4, 5 and 6 are like wise combined to form a single installation situated on a ship. A great advantage of the method according to the invention is that the same equipment can be used for various purposes. The heat exchangers on the ship serve both for the liquefying and for the gasifying of the natu ral gas, and this means a substantial reduction in the capital outlay required.

It is to be noted that the method described above can, also be used in transporting gases other than natural gas. These other gases may be, for example, ethane, butane, propane, nitrogen, oxygen, ammonia.

In the example described above isopentane is cited as the fluid for temporarily storing the cold and the heat. However, other suitable materials can also be used for this purpose, for example isobutane, Water mixed with at least one freezing point depressant, e.g., water mixed with ammonia or water mixed with alcohol, or mixtures of hydrocarbons such as, for example, a mixture of isopentane and isobutane.

In the above example a ship is cited as the vehicle. In place of a ship, land vehicles can also be used, for example one or more rail cars or road tankers.

The cold fluid, for example the cold isopentane, can be stored in the ship in the heatinsulated tanks which are used for storing the liquefied natural gas. This is possible since, when the ship is sailing from the importing port to the exporting port, these tanks are free from liquefied natural gas. The Warm isopentane can be stored in normal, i.e. nonheat insulated ships tanks.

I claim as my invention:

1. A method of transporting a gas, particularly natural gas or methane, by means of a vehicle from a reception point to a delivery point comprising:

supplying a gas to the vehicle at the reception point;

removing suflicient heat from said gas to lequefy same at least partly by heat exchanging said gas with a fluid in substantially the liquid state;

passing the liquefied gas into tanks carried by the vehicle;

passing the heat exchange fluid in substantially the liquid state into tanks carried by the vehicle; transferring the vehicle from the reception point to the delivery point;

supplying sufficient heat to said gas to gasify same abroad the vehicle at the delivery point at least partly by heat exchanging said gas with said heat exchange fluid in substantially the liquid state;

discharging the gasified gas from the vehicle at the delivery point; and

passing the heat exchange fluid in substantially the liquid state into tanks carried by the vehicle for return to the reception point.

2. A method for transporting gas as defined in claim 1 wherein the heat exchange fluid is isopentane.

3. A method for transporting gas as defined in claim 1 wherein the heat exchange fluid is water mixed with at least one freezing point depressant.

4. A method for loading a vehicle at a reception point with a gas, particularly natural gas or methane, comprising:

supplying a gas to the vehicle at the reception point;

liquefying the gas supplied to the vehicle at least partly by bringing the gas into heat exchange with a colder liquefied fluid which is present in tanks carried by the vehicle;

passing the liquefied gas into tanks carried by the vehicle; and

passing the liquefied fluid which remains in substantially the liquid state after heat exchange with the gas into tanks carried by the vehicle.

5. A method for the unloading at the delivery point of a vehicle loaded with liquefied gas, particularly natural gas or methane, comprising:

converting the liquefied gas into the gaseous state abroad the vehicle at the delivery point, at least partly by bringing the liquefied gas into heat exchanging with a warmer fluid in substantially the liquid state which is present in tanks carried by the vehicle;

7 discharging the gas from the vehicle at the delivery point; and passing the fluid which remains in substantially the liquid state after heat exchange with the gas into tanks carried by the vehicle.

2,799,997 7/1957 Morrison 6254 X 6/1960 Morrison 6224OX 8 2,975,608 3/1961 Morrison 62-55 X 3,018,632 1/1962 Keith 62-55 X FOREIGN PATENTS 879,856 10/1961 Great Britain.

OTHER REFERENCES Advances in Cryogenic Engineering, vol. 5, Plenum Press, Inc. New York, 1960-TP 480 A3 C2 (pp. 338- 345 relied on).

LLOYD L. KING, Primary Examiner. 

